1. Field of the Invention
This invention relates to an apparatus for chipping large pieces of wood such as logs into small chips and, in particular, to a wood chipper which captures and chips oversized wood pieces, so-called slivers, which are not initially chipped.
2. Description of the Related Art
Conventional wood chipping machines are exemplified by the disclosure of U.S. Pat. No. 3,069,101 to Wexell. Such machines have a horizontal axis about which a cutter disk rotates. A housing surrounds the rotating disk and there is generally one or more infeed chutes through which wood is fed to contact, and be chipped by, cutting blades mounted on the cutter disk. There is also one or more means for outputting the chipped wood from the housing. Typically, chips are blown from the chipper by air which is forced through an exhaust chute, although they may simple drop to a conveyor below the cutter disk.
The cutter disk has a plurality of straight slots, each extending radially from near the center of the disk towards the periphery of the disk. A cutting blade is mounted to one side of the disk adjacent each slot. The cutting blade extends the length of the slot and its cutting edge protrudes from the surface of the disk. The side of the disk having the protruding cutting edges is the front or cutting side of the disk which contacts and chips, incoming logs or other wood parts. As a rotating blade contacts a log, the blade slices the wood, forming chips which pass through the respective slot in the disk to the back side of the disk referred to as the discharge side, where the chip is blown or otherwise removed from the chipper housing.
The logs to be chipped are infed by a conveyor or other means until the log contacts the disk. Typically, the logs or wood pieces are not infed at an angle perpendicular to the surface of the disk, but rather at an acute angle thereto, so they generally are directed towards the vertical axis of the disk. The logs contact the cutting disk and the blades of the disk slice off chips from the end of the log. The chips are severed from the log by the blades of the disk as they pass a stationary anvil or wear plate. The anvil or wear plate is attached to an anvil support which extends from the housing or interior side of the infeed chute towards the cutter disk. The anvil or wear plate edge extends from the support so that there is only a small gap between the anvil edge and the rotating blades of the cutting disk, thus defining a cutting interface between the blades and the anvil. The gap between the anvil and the blades is generally about 0.0001 to 0.00005 of an inch. The anvil edge acts as a cutting surface for the rotating blades to cut against. The chipper is self feeding in that the impact and cutting action of each successive blade pulls the log or wood pieces to the disk so as to be in position for the next cutting blade.
Occasionally, instead of properly severing chips from the log, the cutting blade will draw a sliver of wood past the anvil through the small gap between the anvil and the cutting blades. The sliver is typically of the relatively tough wood from the outer surface of the log, just under the bark. This tough wood tends to split from the side of the log and be pulled through the gap between the anvil and blades rather than be properly cut by the blades. The resulting slivers are often considerably thicker than the width of the gap due to the deformability of the wood and possibly deflection of the disk. The sliver may be up to 1/8 of an inch thick and may be as much as a few feet long because the blades can successively and continuously draw the unchipped sliver through the blade/anvil gap. Once a piece of wood passes between the anvil and the knit it is inside the housing and can freely move to the discharge side of the disk. The large unchipped slivers can then be exhausted with the other chipped material. The result is that the chips created from the logs are contaminated with oversize slivers which must be later separated and separately rechipped or otherwise processed further.
With conventional chippers there is no way to prevent large unchipped slivers from becoming mixed with the desirable wood chips.